With the generation of accelerators, boron neutron capture therapy (BNCT) technology entered a stage of rapid development. Neutrons with different energies produced by the proton produced by the accelerator interacting with the target or generated through the nuclear reaction. These neutrons are moderated by a beam shaping assembly to epithermal neutrons at a key energy level, and further become thermal neutrons after into the human body. The thermal neutrons react with the boron-containing pharmaceuticals in the tumor cells, and the radiation energy thereof can destroy the tumor cells. The killing range is restricted at the cells' level and there is almost no harm to normal tissues.
The neutrons produced from the target have a wide range of energy distributions including thermal neutrons, epithermal neutrons and fast neutrons, the radiation beam also includes γ rays which do not contribute to the treatment and result in a larger proportion of nonselective dose deposition in normal tissue, and the more the proportion of nonselective dose deposition in normal tissue is, the greater the damage to normal tissue is. One of the applications of moderation materials in beam shaping assembly as the neutron moderation material is the key to improving beam quality and reducing the amount of unwanted rays in the treatment. Therefore, the moderation material in the beam shaping assembly becomes the hotspot in the field of BNCT technology, and the advantages and disadvantages of neutron moderation material are mainly reflected by the neutron beam quality. The neutron beam quality is divided into air beam quality and prosthesis beam quality, wherein the air beam quality can be evaluated synthetically by epithermal neutron beam flux, fast neutron contamination, γ ray contamination, thermal to epithermal neutron flux ratio and neutron forwardness, while the prosthesis beam quality is reflected by the dose distribution of the beam in the prosthesis and the therapeutic effect of the beam in the prosthesis. In addition to the advantage depth (AD), advantage depth dose rate (ADDR) and advantage dose rate (AR) and treatment time as prosthesis beam quality factors, using 30.0 RBE-Gy treatable depth can better reflect the maximum advantage depth of cancer.
The screening of neutron moderation materials for the prosthesis beam quality has not been found, yet.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.